12,464 research outputs found
Matching Kasteleyn Cities for Spin Glass Ground States
As spin glass materials have extremely slow dynamics, devious numerical
methods are needed to study low-temperature states. A simple and fast
optimization version of the classical Kasteleyn treatment of the Ising model is
described and applied to two-dimensional Ising spin glasses. The algorithm
combines the Pfaffian and matching approaches to directly strip droplet
excitations from an excited state. Extended ground states in Ising spin glasses
on a torus, which are optimized over all boundary conditions, are used to
compute precise values for ground state energy densities.Comment: 4 pages, 2 figures; minor clarification
Random pinning limits the size of membrane adhesion domains
Theoretical models describing specific adhesion of membranes predict (for
certain parameters) a macroscopic phase separation of bonds into adhesion
domains. We show that this behavior is fundamentally altered if the membrane is
pinned randomly due to, e.g., proteins that anchor the membrane to the
cytoskeleton. Perturbations which locally restrict membrane height fluctuations
induce quenched disorder of the random-field type. This rigorously prevents the
formation of macroscopic adhesion domains following the Imry-Ma argument [Y.
Imry and S. K. Ma, Phys. Rev. Lett. 35, 1399 (1975)]. Our prediction of
random-field disorder follows from analytical calculations, and is strikingly
confirmed in large-scale Monte Carlo simulations. These simulations are based
on an efficient composite Monte Carlo move, whereby membrane height and bond
degrees of freedom are updated simultaneously in a single move. The application
of this move should prove rewarding for other systems also.Comment: revised and extended versio
Zero-temperature random-field Ising model on a bilayered Bethe lattice
Peer reviewedPublisher PD
Mobile Computing in Physics Analysis - An Indicator for eScience
This paper presents the design and implementation of a Grid-enabled physics
analysis environment for handheld and other resource-limited computing devices
as one example of the use of mobile devices in eScience. Handheld devices offer
great potential because they provide ubiquitous access to data and
round-the-clock connectivity over wireless links. Our solution aims to provide
users of handheld devices the capability to launch heavy computational tasks on
computational and data Grids, monitor the jobs status during execution, and
retrieve results after job completion. Users carry their jobs on their handheld
devices in the form of executables (and associated libraries). Users can
transparently view the status of their jobs and get back their outputs without
having to know where they are being executed. In this way, our system is able
to act as a high-throughput computing environment where devices ranging from
powerful desktop machines to small handhelds can employ the power of the Grid.
The results shown in this paper are readily applicable to the wider eScience
community.Comment: 8 pages, 7 figures. Presented at the 3rd Int Conf on Mobile Computing
& Ubiquitous Networking (ICMU06. London October 200
Zeeman Relaxation of Cold Atomic Iron and Nickel in Collisions with 3He
We have measured the ratio of the diffusion cross-section to the angular
momentum reorientation cross-section in the colliding Fe-3He and Ni-3He
systems. Nickel (Ni) and iron (Fe) atoms are introduced via laser ablation into
a cryogenically cooled experimental cell containing cold (< 1 K) 3He buffer
gas. Elastic collisions rapidly cool the translational temperature of the
ablated atoms to the helium temperature. The cross-section ratio is extracted
by measuring the decays of the atomic Zeeman sublevels. For our experimental
conditions, thermal energy is comparable to the Zeeman splitting. As a result,
thermal excitations between Zeeman sublevels significantly impact the observed
decay. To determine the cross-section ratio accurately, we introduce a model of
Zeeman state dynamics that includes thermal excitations. We find the
cross-section ratio for Ni-3He = 5 x 10^3 and Fe-3He <= 3 x 10^3 at 0.75 K in a
0.8 T magnetic field. These measurements are interpreted in the context of
submerged shell suppression of spin relaxation as studied previously in
transition metals and rare earth atoms.Comment: 10 pages, 5 figures; submitted to Phys. Rev.
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Tillamook prehistory and its relation to the Northwest coast culture area
Laterally driven interfaces in the three-dimensional Ising lattice gas
We study the steady state of a phase-separated driven Ising lattice gas in
three dimensions using computer simulations with Kawasaki dynamics. An external
force field F(z) acts in the x direction parallel to the interface, creating a
lateral order parameter current j^x(z) which varies with distance z from the
interface. Above the roughening temperature, our data for `shear-like' linear
variation of F(z) are in agreement with the picture wherein shear acts as
effective confinement in this system, thus supressing the interfacial
capillary-wave fluctuations. We find sharper magnetisation profiles and reduced
interfacial width as compared to equilibrium. Pair correlations are more
suppressed in the vorticity direction y than in the driving direction; the
opposite holds for the structure factor. Lateral transport of capillary waves
occurs for those forms of F(z) for which the current j^x(z) is an odd function
of z, for example the shear-like drive, and a `step-like' driving field. For a
V-shaped driving force no such motion occurs, but capillary waves are
suppressed more strongly than for the shear-like drive. These findings are in
agreement with our previous simulation studies in two dimensions. Near and
below the (equilibrium) roughening temperature the effective-confinement
picture ceases to work, but the lateral motion of the interface persists.Comment: 20 pages, 11 figures, submitted to Phys. Rev.
Universality in phase boundary slopes for spin glasses on self dual lattices
We study the effects of disorder on the slope of the disorder--temperature
phase boundary near the Onsager point (Tc = 2.269...) in spin-glass models. So
far, studies have focused on marginal or irrelevant cases of disorder. Using
duality arguments, as well as exact Pfaffian techniques we reproduce these
analytical estimates. In addition, we obtain different estimates for spin-glass
models on hierarchical lattices where the effects of disorder are relevant. We
show that the phase-boundary slope near the Onsager point can be used to probe
for the relevance of disorder effects.Comment: 8 pages, 6 figure
Use of grid tools to support CMS distributed analysis
In order to prepare the Physics Technical Design Report, due by end of 2005, the CMS experiment needs to simulate, reconstruct and analyse about 100 million events, corresponding to more than 200 TB of data. The data will be distributed to several Computing Centres. In order to provide access to the whole data sample to all the world-wide dispersed physicists, CMS is developing a layer of software that uses the Grid tools provided by the LCG project to gain access to data and resources and that aims to provide a user friendly interface to the physicists submitting the analysis jobs. To achieve these aims CMS will use Grid tools from both the LCG-2 release and those being developed in the framework of the ARDA project. This work describes the current status and the future developments of the CMS analysis system
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